A number of fiber reinforced plastics are used commercially for various purposes. Articles such as sheets, tapes, or fabrics wherein fibers are impregnated with a resin such as an epoxy resin are referred to as "prepreg substrates". One important use of prepreg substrates is to provide a surface upon which a pattern of an electrical conductor can be provided to obtain circuit boards or circuit cards. The printed circuit boards or printed circuit cards are prepared from laminates of multiple layers of the fiber impregnated epoxy resin compositions. These laminates need to be resistant to various solvents since they are repeatedly exposed to processing solvents and vapors thereof. For instance, in many instances photoresists are stripped from the surface of metal, bonded to the surface of a laminate by exposing the photoresist to solvents which can cause leaching and softening of various materials.
Moreover, it is desired that the laminates be selfextinguishing and that the epoxy employed act as a fire retardant. The materials also should have a high heat distortion temperature in order to avoid warpage when exposed to high processing temperatures.
A further requirement for the epoxy composition is that it have sufficient adhesive power for bonding metal film to the surface of the laminate.
A still further concern is to provide tenacious adhesion between the fibrous substrate and the epoxy composition.
In order to enhance the adhesion between the epoxy composition and fibrous substrate, the substrates have been coated with silanes. Although the use of silanes and especially aminosilanes has proved to provide quite good adhesion with the epoxy compositions, there still remains room for additional enhancement in the bonding strength between the epoxy and the fibrous substrate.
In particular, the bond between the fibers and epoxy, although sufficient for many prepreg applications, permits some slippage of the fibers during the lamination process. This slippage, in turn, can cause dimensional movement of the epoxy-fiber laminate in the warp and fill directions.